This invention relates to the method and apparatus for purifying or cleaning molten aluminum by means of gas sparging.
The practice of sparging molten metal by passing gas upwardly through a moving stream of such metal in order to purify or clean impurities from the stream of metal has been taught by various prior art patents. For example, Blayden, et al in U.S. Pat. No. 3,737,305 discloses apparatus for passing a fluxing gas through molten aluminum as the aluminum moves through a bed of refractory bodies. The molten aluminum flows through a refractory bed and under a baffle positioned in the molten metal stream. As the metal flows under the baffle, a stream of fluxing gas is introduced to bubble upwardly through the refractory bed and the molten metal on the upstream side of the baffle. The fluxing gas interacts with impurities in the aluminum and transports the impurities to the top of the molten stream on the upstream side of the baffle. The impurities may then be skimmed from the molten metal.
Montgrain in U.S. Pat. No. 4,290,590 discloses another apparatus for gas sparging wherein gas bubbles are directed upwardly through a series of spaced nozzles arranged in a trough or furnace. The nozzles are arranged to prevent lateral spread of the bubbles and to hold down bubble size thereby increasing the efficiency of the sparging apparatus. Dantzig, et al in U.S. Pat. No. 4,298,187 discloses yet another apparatus for gas sparging. The Dantzig et al device includes a baffle positioned in the path of a stream of molten metal flow. Gas is bubbled upwardly through a special nozzle discharge device on the upstream side of the baffle.
While the aforesaid gas sparging apparatus appear to be quite useful, improved methods and apparatus for purifying or cleaning molten metals have been sought. This is especially true with respect to molten aluminum. The present invention relates to such an improved apparatus and method.